1. Field of the Invention
The present invention relates to a honeycomb structural body that is used as a filter for removing particulates and the like contained in exhaust gases discharged from an internal combustion system such as a diesel engine or the like, a catalyst supporting member and the like.
2. Discussion of the Background
In recent years, particulates, such as soot and the like, contained in exhaust gases that are discharged from internal combustion engines of vehicles, such as buses, trucks and the like, and construction machines and the like, have raised serious problems as those particulates are harmful to the environment and the human body.
In order to solve these problems, various honeycomb structural bodies made of porous ceramics, which serve as filters capable of collecting particulates in exhaust gases to purify the exhaust gases, have been proposed.
Conventionally, with respect to the honeycomb structural body of this type, a honeycomb structural body comprising: a ceramic block in which a plurality of honeycomb units are bonded to each other through a sealing material layer, said honeycomb unit is mainly composed of porous ceramic and includes a large number of through holes placed in parallel with one another in a longitudinal direction with a partition wall interposed therebetween; and a sealing material layer formed on a peripheral portion thereof, has been known.
With respect to these honeycomb structural bodies, most of them have a circular shape on the cross section perpendicular to the longitudinal direction; however, in recent years, honeycomb structural bodies having various shapes on the cross section perpendicular to the longitudinal direction, such as an elongated round shape (race-track shape), an elliptical shape, an approximately triangular shape, an approximately trapezoidal shape and the like, have been proposed (for example, see Japanese Patent Laid-Open Publication No. 2002-273130, Japanese Patent Laid-Open Publication No. 2003-260322, International Laid-Open Publication No. 03/078026A1, and Japanese Patent Laid-Open Publication No. 2003-181233).
FIG. 1A is a perspective view that schematically shows a honeycomb filter formed by such a honeycomb structural body, and FIG. 1B is a partially enlarged perspective view that shows one portion thereof. Moreover, FIG. 2A is a perspective view that schematically shows one example of a honeycomb unit that forms the honeycomb filter shown in FIGS. 1A and 1B, and FIG. 2B is a cross-sectional view taken along line A-A of FIG. 2A.
As shown in FIG. 1A, a honeycomb filter 100 has a structure in which a plurality of honeycomb units 110 made of silicon carbide or the like are combined with one another to form a ceramic block 105 through a sealing material layer (an adhesive layer) 101, with a sealing material layer (a coat layer) 102 being formed on the periphery of this ceramic block 105. The end face of this honeycomb filter 100 has an elongated round shape, and the pattern of the sealing material layer (the adhesive layer) among the honeycomb units on the cross-section perpendicular to the longitudinal direction is designed so as to be approximately perpendicular to the major axis of the shape forming the contour of the cross section.
As shown in FIGS. 2A and 2B, in the honeycomb unit 110, a number of through holes 111 are placed in parallel with one another in the longitudinal direction so that the partition wall 113 that separates the through holes 111 from each other is allowed to function as a filter. In other words, as shown in FIG. 2B, each of the through holes 111 formed in the honeycomb unit 110 is sealed with a plug 112 at either of ends of its exhaust gas inlet side and outlet side so that exhaust gases that have entered one through hole 111 are discharged from another through hole 111 after having always passed through the partition wall 113 that separates the corresponding through holes 111.
Upon manufacturing such a honeycomb structural body having an elliptical shape on its cross section perpendicular to the longitudinal direction, first, after having manufactured honeycomb units each of which is made of porous ceramics with its end face being sealed so as to form a checked pattern as shown in FIGS. 2A and 2B, these pluralities of honeycomb units are bonded to one another through sealing material, and dried to form a honeycomb unit aggregated body.
Next, this honeycomb unit aggregated body is subjected to a cutting process such that the cross section perpendicular to the longitudinal direction is formed into an elongated round shape, and at this time, the cutting process is carried out so that in the elongated round shape, the pattern of the sealing material layer (the adhesive layer) among the honeycomb units on the cross section is designed so as to be approximately perpendicular to the major axis of the shape forming the contour of the cross section, and a sealing material layer (a coat layer) is lastly formed on the periphery thereof, and dried; thus, the manufacturing process of the honeycomb filter is completed.
The above-mentioned document has described that the honeycomb structural body having such a shape exerts such effects that it can suppress a reduction in resistance against canning (canning strength).
In the honeycomb filter shown in FIGS. 1A and 1B, however, in the cross section perpendicular to the longitudinal direction, the sealing material layer (the adhesive layer) is formed with an approximately right angle with respect to the major axis of the elliptical shape forming the contour of the cross section, and the sealing material layer (the adhesive layer) formed with the right angle with respect to the major axis is comparatively short. Such a short length of the sealing material layer may cause a problem.
The contents of Japanese Patent Laid-Open Publication No. 2002-273130, Japanese Patent Laid-Open Publication No. 2003-260322, International Laid-Open Publication No. 03/078026A1, and Japanese Patent Laid-Open Publication No. 2003-181233 are incorporated herein by reference in their entirety.